This invention relates generally to an ink jet printing apparatus and, in particular, to an ink jet print head in which melted ink is ejected through nozzles onto a recording medium such as paper to form characters and images.
An ink jet printer in which ink is ejected from nozzles onto a recording medium to form characters and images is described in U.S. Pat. No. 4,072,959. This patent describes an apparatus in which the outlet ends of a plurality of nozzles are mounted on a nozzle plate and the inlet ends of the nozzles are emersed in ink. The inlets are positioned adjacent to a plurality of corresponding piezoelectric transducers that are also disposed in the ink so that piezoelectrically induced oscillations from the transducers will propel the ink through the nozzles onto a recording medium.
The piezoelectric transducers are formed with vibrators that are arranged and positioned to produce oscillating movement in a direction perpendicular to the plane of the nozzle plate. The ink flow passageways leading to the respective nozzle inlets are short. An ink jet printing apparatus constructed in accordance with the above description can insure enhanced efficiency and stability in propelling ink drops from the nozzles. Only minimal electricity is required to cause the vibrators to sufficiently propel ink through the nozzles for printing.
Conventional ink jet printers of this type have certain limitations and deficiencies, however. For example, because the piezoelectric transducers must be submerged in liquid ink, the ink is typically a nonconductive oil-based ink having organic solvents as main ingredients. Consequently, inadequate printing quality occurs when the ink is propelled onto grainy paper. The ink bleeds into the paper which blurs the print or thins out locally which also adversely affects print quality.
Japanese Laid Open Patent No. 61-98547 describes an ink jet recording apparatus that eliminates inadequacies of ink jet printing with conventional liquid ink. The ink jet printer described in this Japanese patent publication utilizes hot melt ink to enhance printing quality. A critical inadequacy associated with ink jet printing with hot-melt ink is that when the ink changes phase from solid to liquid, air bubbles become trapped in the liquid ink. In extreme cases, the air bubbles can be present to such an extent in critical locations that they absorb the oscillating force from the piezoelectric transducers and prevent proper ink ejection. The configuration of conventional hot-melt ink print heads does not lead to effective dispersion of bubbles.
Conventional ink jet printers therefore have inadequacies due to these shortcomings. Accordingly, it is desirable to provide an improved ink jet printing apparatus which avoids the shortcomings of the prior art and prints clear uniform characters and images on a wide range of recording media.